The intersection will consist of only one point.
A line is produced
If a right circular cone is intersected by a plane so that the intersection goes through the cone's vertex as well as an edge of each nappe, the shape produced is a line. Not asked, but... If the angle of the plane is less than the angle of the cone, then the intersection is a point. If the angle of the plane is greater than the angle of the cone, then the intersection is two lines intersecting at the vertex. If the plane insersects at other than the vertex, then the intersection is a circle when the plane is perpendicular to the cone's axis, an ellipse when the plane's angle is less than the cone's angle, a parabola when the planes's angle equals the cone's angle, and two hyperbole's in the last case.
A shape with a circular base and a vertex that isn't in the same plane as the base is called a cone.
if a right circular cone intersects a plane that goes through both nappes of the cone, but not through the vertex, the resulting curve will be a hyperbola
The following are some examples of a shape with two flat face and one curved surface: A sphere intersected by two planes. An ellipsoid intersected by two plane faces. A paraboloid intersected by two plane faces. A cone intersected by two plane faces. A cylinder. A hyperboloid intersected by two plane faces.
An Ellipse
A point.
A line is produced
If I understand your description correctly, a line.
It will be a hyperbola.
hyperbola
hyperbola
The answer will depend on the angle formed between the plane and the axis of the cone. Since there is no picture "below" it is not possible to determine that and therefore it is impossible to give an answer.
If a right circular cone is intersected by a plane so that the intersection goes through the cone's vertex as well as an edge of each nappe, the shape produced is a line. Not asked, but... If the angle of the plane is less than the angle of the cone, then the intersection is a point. If the angle of the plane is greater than the angle of the cone, then the intersection is two lines intersecting at the vertex. If the plane insersects at other than the vertex, then the intersection is a circle when the plane is perpendicular to the cone's axis, an ellipse when the plane's angle is less than the cone's angle, a parabola when the planes's angle equals the cone's angle, and two hyperbole's in the last case.
An ellipse is produced.
A sphere intersected by a plane, An circular ellipsoid intersected by a plane, A cylinder, A cone, and many more shapes, some of which don't even have a name!
A shape with a circular base and a vertex that isn't in the same plane as the base is called a cone.